Seat force sensor for a patient support

ABSTRACT

A weighing system associated with a mattress and configured to measure a patient&#39;s weight while the patient is positioned on the mattress.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/US2004/041358, which has aninternational filing date of Dec. 10, 2004, designating the UnitedStates of America, and claims the benefit of U.S. Provisional PatentApplication No. 60/529,198, which was filed Dec. 12, 2003. Thedisclosures of each of these prior applications are hereby incorporatedby reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a weighing system for sensing apatient's weight when the patient is positioned on a patient supportsuch as a hospital bed.

Some patients may be confined to a bed for extended periods of timemaking it difficult to weigh the patient on conventional weighingscales. Other patients may be wholly or partially disabled and unable tobe positioned on a conventional weighing scale. The present inventionprovides a weighing system which can be added to or incorporated into amattress and has the ability to accurately measure a patient's weightwhile the patient is positioned on the patient support. The weighingsystem can also provide the patient weight data to other systems, suchas an air pressure controller for an inflatable mattress supporting thepatient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view, in partial schematic, of a patientsupport;

FIG. 2 is a partially exploded side elevational view, in partialschematic, of an illustrative embodiment of a mattress assembly inaccordance with the present invention;

FIG. 3 is a cross-sectional view, in partial schematic, taken along line3-3 of FIG. 1 of another embodiment of a mattress assembly;

FIG. 4 is a cross-sectional view, in partial schematic, similar to FIG.3, of another embodiment of a mattress assembly;

FIG. 5 is a cross-sectional view, in partial schematic, similar to FIG.3, of another embodiment of a mattress assembly;

FIG. 6 is a block diagram of an illustrative embodiment of a patientweighing system;

FIG. 7 is a flow chart showing an illustrative method of weighing apatient;

FIG. 8 is an illustrative chart of pressure versus pounds used forcorrelating the internal pressure of a seat force sensor with theapproximate patient weight;

FIG. 9 is a block diagram of a further illustrative embodiment of apatient weighing system;

FIG. 10 is a flow chart showing another illustrative method of weighinga patient;

FIG. 11 is a flow chart showing a further illustrative embodiment ofweighing a patient;

FIG. 12 is a cross-sectional view, in partial schematic, of anotherembodiment of a patient support assembly;

FIG. 13 is a cross-sectional view, in partial schematic, of anotherembodiment of a patient support assembly;

FIG. 14 is a partially exploded side elevational view, in partialschematic, of another embodiment of a weight sensor of the presentinvention;

FIG. 15 is a partially exploded side elevational view, in partialschematic, of a further illustrative embodiment of a weight sensor ofthe present invention;

FIG. 16 is a partially exploded side elevational view, in partialschematic, of an illustrative embodiment of a mattress assemblyincluding the weight sensor shown in FIG. 15;

FIG. 17 is a cross-sectional view, in partial schematic, of anotherembodiment of a mattress assembly including the weight sensor shown inFIG. 15;

FIG. 18 is a cross-sectional view, in partial schematic, of anotherembodiment of a mattress assembly including the weight sensor shown inFIG. 15;

FIG. 19 is a cross-sectional view, in partial schematic, of anotherembodiment of a mattress assembly including the weight sensor shown inFIG. 15;

FIG. 20 is a cross-sectional view, in partial schematic, of anotherembodiment of a patient support assembly including weight sensorssimilar to the one shown in FIG. 15; and

FIG. 21 is a cross-sectional view, in partial schematic, of anotherembodiment of a patient support assembly including the patient weightsensor shown in FIG. 15.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a patient support 2 including a frame 4, a deck 6,and an illustrative mattress assembly 10 is shown. The mattress assembly10 may be utilized in connection with any type of conventional patientsupport 2, such as a hospital bed, a stretcher, etc. Referring now toFIG. 2, mattress assembly 10 illustratively includes a fluid mattress orsupport 12, a collector plate 16, a seat force sensor 18, and a basesupport 14. In various embodiments, fluid mattress 12 and base support14 include air bladders, foam sections or any other suitable form ofmattress material. In one illustrative embodiment, fluid mattress 12includes at least one inflatable air bladder 19 having a head section26, a seat section 22, and a foot section 24. In certain embodiments,the head section 26, seat section 22, and foot section 24 are fluidlyseparated by walls 27. In one illustrative embodiment, base support 14includes a hard foam material, while fluid mattress 12 includes aplurality of air bladders 19 such as those described in U.S. Pat. Nos.6,295,657 and 6,584,528, the disclosures of which are expresslyincorporated by reference herein. In another illustrative embodiment,mattress 12 and base support 14 both comprise a foam material. In afurther embodiment, the air bladders 19 of the mattress 12 include foammaterial.

As shown in FIG. 2, collector plate 16 is illustratively positionedabove seat force sensor 18 and under the seat section 22 of fluidmattress 12. Collector plate 16 is configured to substantially support apatient's entire seat region to substantially direct, focus and/oruniformly apply the patient's weight to seat force sensor 18. Collectorplate 16 is illustratively made of metal, plastic, wood, foam, or anyother suitable rigid or semi-rigid material. The collector plate 16could also comprise an inflated air bladder. In one illustrativeembodiment, seat force sensor 18 is a single air bladder placed undercollector plate 16. Seat force sensor 18 can be any form of conventionalair bladder, and its dimensions are sufficiently long and wide enough sothat the patient's sacral or seat region substantially covers thebladder area. Seat force sensor 18 may also include internal baffles 30so it is able to maintain a predictable shape and volume as internalpressure increases. The air bladder thickness of the seat force sensor18 is sufficiently thin so that the inflation of the air bladder willnot be an annoyance to a patient positioned thereabove.

Referring now to FIG. 3, a further illustrative mattress assembly 109,including seat force sensor 18, is shown. Fluid mattress or support 129is shown positioned on base support 14 of mattress assembly 109.Mattress assembly 109 is supported by deck 6 of patient support 2. Inthis embodiment, fluid mattress 129 of the mattress assembly 109includes one or more air bladders 19. Seat force sensor 18 and collectorplate 16 are positioned within air bladder 19 of fluid mattress 129.More particularly, seat force sensor 18 and collector plate 16 arepositioned below the patient's sacral or seat region while positionedwithin air bladder 19 of fluid mattress 129. In another illustrativeembodiment, seat force sensor 18 is used without a collector plate 16.

In another alternative embodiment of mattress assembly 100, as shown inFIG. 4, seat force sensor 18 is positioned on top of fluid mattress 120.In this position, seat force sensor 18 is directly beneath a patientpositioned on mattress assembly 100.

In yet another embodiment of mattress assembly 10′″ as shown in FIG. 5,base support 149 includes a seat force sensor 18 which is positionedwithin the base support 149. Collector plate 16 (not shown) could alsobe positioned inside base support 149 above seat force sensor 18 in thisembodiment. In addition to the embodiments described above, seat forcesensor 18 may be removably coupled to existing mattresses or patientsupports or incorporated in a fixed orientation into new patientsupports.

Referring now to FIG. 6, a schematic of an illustrative embodimentoperating system 31 including seat force sensor 18 is shown. Acontroller 33 is coupled to an air source, such as an air compressor 32,by signal line 40. If mattress assembly 10 is equipped with aircompressor 32 configured to inflate the mattress 12, then such an aircompressor 32 can also be used to inflate seat force sensor 18. Aircompressor 32 is coupled to seat force sensor 18 by air line 42 which,in turn, is coupled to intake valve 36 b. Intake valve 36 b is coupledto intermediate air line 42 and air line 44 to prevent undesired leakageof air from seat force sensor 18 through compressor 32. Exhaust valve 36a is coupled to seat force sensor 18 by air line 44 and includes anexhaust to the atmosphere 37. Controller 33 is coupled to exhaust valve36 a by signal line 46 a, and is in communication with intake valve 36 bthrough signal line 46 b. A pressure transducer 38 is coupled to seatforce sensor 18 by air line 48. Pressure transducer 38 is also coupledto controller 33 by signal line 50. A conventional flow restrictor (notshown) may be used as a flow control for the output of the aircompressor 32.

One illustrative method of operating the system 31 to determine theapproximate patient weight is based upon measuring the change in thepressure in seat force sensor 18 when it has been inflated with a knownamount of air. For this method, the same amount of air is placed in seatforce sensor 18 for all patients positioned on mattress assembly 10. Thepressure of the bladder of seat force sensor 18 can then be measured andcorrelated with an experimentally determined look-up table. For example,a pressure of 20 psi in seat force sensor 18 might correlate with apatient weighing 200 lbs., while a pressure of 17 psi might correlatewith a patient weighing 180 lbs. Since the same amount of air is presentin seat force sensor 18 for all patients, a higher pressure in seatforce sensor 18 indicates a patient is heavier than a patient whocreates a lower pressure in seat force sensor 18.

For the first step of this method, the bladder of seat force sensor 18is first deflated or vented to atmosphere so the amount of air initiallyin the seat force sensor 18 is negligible. Next, a known volume of airis used to inflate the bladder of seat force sensor 18. This can beaccomplished using air compressor 32 that outputs air at a knownvolumetric flow rate. The air compressor 32 is activated for apredetermined amount of time. In this method, the same amount of air ispresent in the seat force sensor 18 for each evaluation.

A flow chart 100 illustrating the steps of the illustrative method isshown in FIG. 7. To determine the patient's weight, seat force sensor 18is positioned below the patient's sacral region in one of the mannersdetailed above. Pressure transducer 38 then measures the pressure inseat force sensor 18 and outputs a signal indicating the pressure tocontroller 33, as shown by step 102. Referring now to step 104, if thepressure in seat force sensor 18 is above a predefined pressure, forexample, 0.2 psi, then controller 33 outputs a signal to valve 36 a todeflate seat force sensor 18 until the pressure in seat force sensor 18is below 0.2 psi, as shown by step 106. When the pressure in seat forcesensor 18 is below the predetermined pressure, controller 30 sends asignal to valve 36 a to close so that seat force sensor 18 can beinflated, as shown by step 108. Next, controller 33 actuates aircompressor 32 to supply air to seat force sensor 18 for a predeterminedamount of time, for example, 5 seconds, again as shown by step 108. Itshould be appreciated that other time intervals could be used and thatthe amount of time during which the air compressor 32 is activateddetermines the volume of air contained within the seat force sensor 18.After the air compressor has been active for the predetermined amount oftime, and shuts down, pressure transducer 38 measures the pressure inseat force sensor 18 and outputs a signal indicative of the pressure tocontroller 33, as shown by step 110.

Referring now to step 112, controller 33 then correlates the pressureindicated by seat force sensor 18 with an approximate patient weight byusing a lookup chart or table, such as that shown in FIG. 8, or by usinga predetermined series of mathematical equations or algorithms. Thecontroller 33 then outputs the approximate patient weight to a display,as shown in step 114, and/or outputs the data to other bed features,such as a mattress air controller for an inflatable bladder 19 in fluidmattress 12, as shown by step 116. For example, as explained below, themattress air controller can then use the patient weight data to selectan appropriate pressure setting for fluid mattress 12. Other bedfunctions, such as a heel pressure relief air bladder and patient turnassist air bladders, may also use the patient weight data to makeadjustments to their respective settings. More particularly, the patientweight data may be used to determine proper pressure settings for theheel pressure relief air bladder and the turn assist air bladders.

Referring further to FIG. 8, a chart indicating an approximate patientweight compared to the pressure in seat force sensor 18 is shown. Line70 connecting data set 72 represent experimental values that have beendetermined based upon the air compressor 32 being activated for 5 secondpredetermined time periods. As noted above, other suitable time periodscould be used.

Patients of different sizes require different pressure settings whenpositioned on inflatable mattresses to prevent pressure ulcers. Onemethod of setting the appropriate pressure setting for an inflatablemattress 12 is for a healthcare provider to approximate or guess thepatient's weight or reference the patient's last recorded weight andinput this data into a controller which then adjusts the pressure in theinflatable mattress 12 for a patient of that weight based on a lookuptable. According to the present invention, the optimum pressure settingfor the inflatable mattress 12 may be determined automatically when apatient enters the bed 2 by determining the patient weight using theseat force sensor 18. As represented by step 116 in FIG. 7, inflatablemattress 12 can receive the patient weight data directly from controller33 so the proper pressure setting may be selected.

The controller 33 also looks for a pressure change within the seat forcesensor 18 at decision step 118. Upon detection of such a pressurechange, an exit detection sub-routine is initiated at block 200, asdetailed below. If no pressure change is detected at step 118, then theprocess continues at block 120 where the controller 33 controls valves36 a and 36 b to hold air pressure in the seat force sensor 18. Thepressure in the seat force sensor 18 is measured and the process thenreturns to decision step 118.

Referring now to FIG. 9, a schematic of an alternative embodimentoperating system 35 is shown. In system schematic 35, controller 33 iscoupled to valve 36 by signal line 52 and to air compressor 32 by signalline 58. Air compressor 32 is coupled to valve 36 by air line 56.Pressure transducer 38 is coupled to seat force sensor 18 by air line62. Controller 33 is also coupled to pressure transducer 38 by signalline 60. Valve 36 is coupled to seat force sensor 18 by air line 54.Valve 36 includes an exhaust to atmosphere 37. In this illustrativeembodiment, valve 36 receives air directly from air compressor 32 andcontrols air flow therefrom to seat force sensor 18, rather than aircompressor 32 being directly connected to seat force sensor 18, as shownin the previous embodiment of FIG. 6.

To determine the approximate patient weight in connection with thesystem 35 of FIG. 9, the method illustrated in FIG. 7 is used with theexception of step 108. More particularly, an alternative step 108 isutilized in connection with system 35. When controller 33 actuates aircompressor 32 to activate for a predetermined amount of time, controller33 also actuates valve 36 to allow air to pass from air compressor 32 toseat force sensor 18. The remaining steps of the method, shown in FIG.7, are substantially as described previously.

Referring now to FIG. 10, associated with the systems 31 and 35 of thepresent invention is a method for detecting when a patient has exitedthe mattress 12 or when the patient or a different patient enters orexits mattress 12. Referring back to FIG. 7, reevaluation of seat force,as shown by step 118, occurs when a pressure change is detected in theseat force sensor 18, for example, due to a patient's change of statussuch as exiting, entering, or repositioning in the bed. Referring toFIGS. 6 and 7, controller 33 monitors the pressure in seat force sensor18 by receiving input from the pressure transducer 38.

In one illustrative embodiment, as shown in FIG. 10, method 200 may beconsidered a subroutine or subprocess which is activated after step 118of method 100 in FIG. 7, if the pressure changes in seat force sensor18. Method 200 includes the step of measuring the pressure (P) in theseat force sensor 18 in step 202. If the pressure in seat force sensor18 drops below a predetermined level (X1) or rises above a predeterminedlevel (X2) as shown by step 204, the process 200 returns to measuringstep 102 of FIG. 7, as shown by block 208. If not, the pressure in theseat force sensor 18 is again monitored for change.

In another illustrative embodiment, shown in FIG. 11, method 220 issimilar to method 200 in that it also monitors the pressure in thebladder at step 222. If the pressure drops to less than a predeterminedlevel of pressure (X1) or rises above a predetermined level (X2) in step224, a one hour timer activates in step 226 and returns to the measuringstep 102 of FIG. 7 after the hour has passed, as shown by step 228. Aswill be appreciated by those of ordinary skill in the art, any suitabletime period may be used. If mattress assembly 10 includes an inflatablemattress 12, this method assumes that pressure ulcers will not form onthe patient within a one hour time period if a new patient has enteredmattress assembly 10 and the pressure in the air mattress 12 is notcorrectly set for the new patient. The one hour time period can beadjusted based on the patient's specific needs.

Other methods of correlating the approximate patient weight with datafrom the seat force sensor 18 may be used. For example, the seat forcesensor 18 could be inflated to a predetermined pressure and theninflated or deflated to a predetermined pressure while the time periodof inflation or deflation is measured. The change in time could then beused to correlate with the approximate patient weight. Another methodmay include the steps of measuring an initial pressure of the seat forcesensor 18 and activating the air compressor 32 to inflate or deflate theair bladder of the seat force sensor 18 until a predetermined volume ofthe air bladder is achieved. The amount of time or the change inpressure could then be used to correlate with the approximate patientweight. To use this method, the volume metric flow rate of the aircompressor 32 would be required. If the amount of air flow out of theair compressor 32 is not predictable or is difficult to determine, theflow can be measured with a flow meter/transducer.

In a further illustrative embodiment of the present invention shown inFIG. 12, an adjustable patient support 300 is shown. Patient support 300includes at least a head section 302 and a seat section 304. Headsection 302 can be elevated to raise a patient positioned on patientsupport 300 to a sitting position. In this embodiment, mattress assembly109 is placed on seat section 304 and a second mattress assembly 306 isplaced on head section 302. Mattress assembly 306 is identical tomattress assembly 109, except that it is positioned on head section 304.Mattress assembly 306 includes a back force sensor 310 and may include acollector plate 312. The back force sensor 310 is substantiallyidentical to the seat force sensor 18, while the collector plate 312 issubstantially identical to the collector plate 16. More particularly,the method of operation for back force sensor 310 is the same methodused to operate seat force sensor 18. Utilizing back force sensor 310and seat force sensor 18 allows a patient positioned on patient support300 to be weighed even when head section 302 is elevated as illustratedin FIG. 12. A controller can compare the pressures in seat force sensor18 and back force sensor 310 to a look-up table to determine thepatient's weight. Alternatively, the values from the seat force sensor18 and back force sensor 310 may be used in algorithms to determine thepatient's weight and position.

It should be noted that the change of pressure detected by the seatforce sensor 18 of the previous illustrated embodiments may be replacedwith a change of pressure detected by the back force sensor 310 totrigger a measurement cycle.

In an alternative embodiment of FIG. 12, back force sensor 310 andcollector plate 312 are not present in mattress assembly 306. Anglesensor 320 is coupled to patient support 300 as shown in FIG. 13 todetermine the angle A of inclination or declination of head section 302relative to seat section 304 and output a signal indicative of the angleA to a controller. The controller then compares the angle A and thepressure in seat force sensor 18 to a look-up table to determine theapproximate patient weight. Again, an algorithm may be substituted forthe look-up table. The weight of a patient positioned on patient support300 can be determined even if head section 302 is inclined or declinedrelative to seat section 304.

It should be noted that a seat force sensor 18 (FIGS. 12 and 13) may beused in combination with a back force sensor 310 (FIG. 12) and an anglesensor 320 (FIG. 13) to determine a patient weight distribution havingimproved accuracy (i.e. detection of a patient sitting up).

Another embodiment of seat force sensor 18 is shown in FIG. 14. Seatforce sensor 400 includes an upper plate 402, a lower plate 404, aplurality of weight sensors 406, wires 408, and a controller 410. Upperplate 402 and lower plate 404 are similar to collector plate 16 and arealso used to concentrate the patient's weight uniformly on the weightsensors 406. Both plates 402 and 404 are illustratively made of metal,plastic, wood, or any other suitable rigid or semi-rigid material.Plates 402 and 404 are sized to support the patient's sacral or seatregion.

Weight sensors 406 are positioned between plates 402 and 404 and producean electrical signal that is proportional to the force applied to them.Weight sensors 406 may include force transducers such as force sensingresistor pads, load cells, resistive ink-type transducers such asFLEXIFORCE by TEKSCAN, or any other suitable force transducer. Anynumber of weight sensors may be used in seat force sensor 400. If moreweight sensors 406 are used in seat force sensor 400, smaller load cellshaving better accuracy can be used which could improve the overallaccuracy of seat force sensor 400. If a smaller number of load cells areused the capacity of each load cell must be greater and as a result, theaccuracy of each load cell is lower which lowers the overall accuracy ofseat force sensor 400.

The plurality of weight sensors 406 are connected to controller 410 bywires 408. In the illustrated embodiment five weight sensors are used.Seat force sensors configured to weigh larger patients may require moreweight sensors 406. Controller 410 receives the electrical signals viawires 408 from each weight sensor 406. Controller 410 then correlatesthe signals received from weight sensor 406 with an approximate patientweight by using a look-up chart or table similar to that shown in FIG. 8or by using a predetermined series of mathematical equations oralgorithms. Controller 410 then outputs the approximate patient weightto a display and/or outputs the data to other bed features, such as amattress air controller for an inflatable bladder in a fluid mattress.As explained above, the mattress air controller can then use the patientweight data to select an appropriate pressure setting for a fluidmattress. Other bed functions, such as a heel pressure relief airbladder and patient turn assist air bladders, may also use the patientweight data to make adjustments to their respective settings.

Another embodiment of seat force sensor 4009 is shown in FIG. 15. Seatforce sensor 4009 is similar to seat force sensor 400 with the exceptionof upper plate 4029 and standoffs 412. Upper plate 4029 includes aplurality of standoffs 412, each positioned directly over one of theplurality of weight sensors 406, which are mounted on lower plate 404.Seat force sensor 4009 includes a standoff 412 for each correspondingweight sensor 406. Standoffs 412 focus the weight of the patient on theweight sensors 406 to provide a more accurate patient weight. Theelectrical signals from the weight sensors 406 are carried to controller410 through wires 408. Any number of weight sensors 406 and standoffs412 could be used in seat force sensor 4009. For illustration, fiveweight sensors 406 are shown in FIG. 15.

As shown in FIG. 16, seat force sensor 4009 is illustratively positionedin the same orientation as seat force sensor 18, shown in FIG. 2. Upperplate 4029 is configured to substantially support a patient's entireseat region and to substantially focus and uniformly apply the patient'sweight to seat force sensor 4009. As discussed above, upper plate 4029is similar to collector plate 16 and is configured to focus the force ofthe patient's weight uniformly upon standoffs 412, which in turn applypressure to weight sensors 406. When the patient is positioned onmattress assembly 10 a, upper plate 4029 is depressed which causesstandoffs 412 to apply pressure to weight sensors 406 to generateelectrical signals proportional to the force applied to them. Controller410 (not shown) receives the electrical signals and correlates them toan approximate patient weight and outputs the patient weight to adisplay and/or other bed features such as a heel pressure relief systemor a patient turn assist system.

Referring now to FIG. 17, a further illustrative mattress assembly 10 bsimilar to mattress assembly 109, shown in FIG. 3, is shown. Fluidmattress or support 12 b is shown positioned on base support 14 ofmattress assembly 10 b. In this embodiment, fluid mattress 12 b ofmattress assembly 10 b includes seat force sensor 4009. Seat forcesensor 4009 is positioned within air bladder 19 of fluid mattress 12 b.More particularly, seat force sensor 4009 is positioned below thepatient's sacral or seat region while positioned within air bladder 19of fluid mattress 12 b.

In another embodiment of mattress assembly 10 c, as shown in FIG. 18,seat force sensor 4009 is positioned on top of fluid mattress 12 csimilar to the embodiment shown in FIG. 4. In this position, seat forcesensor 4009 is directly beneath a patient positioned on mattressassembly 10 c. The patient's sacral region contacts upper plate 4029 andforces standoffs 412 downward applying pressure to weight sensors 406.

In yet another embodiment of mattress assembly 10 d, as shown in FIG.19, base support 14 a includes a seat force sensor 4009 which ispositioned within the base support 14 a which is supported by frame 6.In addition to the embodiments described above, seat force sensor 400may be removably coupled to existing mattresses or patient supports orincorporated in a fixed orientation into new patient supports.

In a further illustrative embodiment of the present invention shown inFIG. 20, an adjustable patient support 300 a is shown. Patient support300 a is similar to patient support 300 shown in FIG. 12. Seat forcesensors 18 have been replaced by seat force sensors 4009. Patientsupport 300a includes at least a head section 302 a and a seat section304 a. Head section 302 a can be elevated to raise a patient position onpatient support 300 a to a sitting position. In this embodiment,mattress assembly 10 b is placed on seat section 304 a and a secondmattress assembly 306 a is placed on head section 302 a. Mattressassembly 306 a is identical to mattress 10 b, except that it ispositioned on head section 304 a. Mattress assembly 306 a includes aback force sensor 4009. Back force sensor 4009 is substantiallyidentical to the seat force sensor 4009. More particularly, the methodof operation of back force sensor 4009 is the same method used tooperate seat force sensor 4009. Utilizing back force sensor 4009 andseat force sensor 4009 allows a patient positioned on patient support300 a to be weighed even when the head section 302 a is elevated asillustrated in FIG. 20. A controller can compare the electrical signalsreceived from weight sensors 406 of seat force sensor 4009 and backforce sensor 4009 to a look-up table to determine the patient's weightor head angle. Alternatively, the electrical signals from seat forcesensor 4009 and back force sensor 4009 may be used in algorithms todetermine a patient's weight.

FIG. 21 illustrates another embodiment of FIGS. 13 and 20, wherein backforce sensor 4009 is not present in mattress assembly 306 b. Anglesensor 320 is coupled to patient support 300 b as shown in FIG. 21 todetermine the angle A of inclination or declination of head section 302b relative to seat section 304 b. Sensor 320 outputs a signal indicativeof the angle A to a controller. The controller then compares the angle Aand the electrical signals received from seat force sensor 4009 to alook-up table to determine the approximate patient weight. Again, analgorithm may be substituted for the look-up table. The weight of thepatient positioned on patient support 300 b can be determined even ifhead section 302 b is inclined or declined relative to seat section 304b.

The foregoing description of the invention is illustrative only, and isnot intended to limit the scope of the invention to the precise termsset forth. Although the invention has been described in detail withreference to certain illustrative embodiments, variations andmodifications exist within the scope and spirit of the invention asdescribed and defined in the following claims.

1. A patient support comprising: a mattress having a head section, afoot section spaced from the head section, and a seat section betweenthe head section and the foot section, the seat section beingdimensioned to support a seat region of a person, an inflatable cellassociated with the seat section, an air source operable to inflate theinflatable cell, a pressure sensor operable to measure pressure in theinflatable cell, a substantially rigid collector plate located above theinflatable cell and arranged to uniformly concentrate a portion of aperson's weight on the inflatable bladder, and a controller operablycoupled to the pressure sensor and to the air source, the controllerbeing operable to automatically determine a value for total body weightof a person positioned on the mattress based on an output of thepressure sensor.
 2. The patient support of claim 1, comprising at leastone baffle in the inflatable cell.
 3. The patient support of claim 1,wherein the mattress includes a plurality of inflatable bladders and thecontroller is configured to signal the air source to adjust the pressureof at least one of the mattress bladders based upon the value for thetotal body weight as determined by the controller from the output of thepressure sensor.
 4. The patient support of claim 1, further comprising asecond inflatable cell associated with the head section of the mattressand a second pressure sensor operable to measure pressure in the secondinflatable cell, wherein the controller is operably coupled to thesecond pressure sensor and is operable to determine the value for thetotal body weight of a person positioned on the mattress based on outputsignal outputs from the first and second pressure sensors.
 5. Thepatient support of claim 4, further comprising an angle sensor coupledto the head section of the mattress to output a signal indicative of theangle of inclination of the head section relative to the seat section,wherein the controller is operable to determine the value for the totalbody weight of a person positioned on the mattress based on the outputsfrom the first and second pressure sensors and the angle sensor outputsignal.
 6. The patient support of claim 1, further comprising an anglesensor coupled to the head section of the mattress to output a signalindicative of the angle of inclination of the head section relative tothe seat section, wherein the controller is operable to determine thevalue for the total body weight of a person positioned on the mattressbased on the output from the pressure sensor and the angle sensor outputsignal.
 7. A patient support comprising: a mattress having a headsection, a foot section spaced from the head section, and a seat sectionbetween the head section and the foot section, the seat section beingdimensioned to support a seat region of a person, at least the footsection including at least one inflatable bladder, an air sourceoperable to inflate the at least one inflatable bladder, a force sensorsized to fit within the dimensions of the seat section of the mattressand configured to output a signal indicative of force applied to theseat section of the mattress, the force sensor comprising asubstantially rigid lower plate, a plurality of force transducers abovethe lower plate, and a substantially rigid upper plate configured toconcentrate a portion of a person's weight on the plurality of forcetransducers thereby to produce the signal, and a controller configuredto receive the output signal from the force sensor and automaticallysignal the air source to adjust pressure in the foot section of themattress based on the output of the force sensor.
 8. The patient supportof claim 7, further comprising a heel pressure relief bladder andwherein the controller is configured to signal the air source to adjustpressure in the heel pressure relief air bladder based on the output ofthe seat section force sensor.
 9. The patient support of claim 7,wherein the plurality of force transducers of the force sensor comprisesa plurality of force sensing resistor pads.
 10. The patient support ofclaim 9, wherein the upper plate positioned above the plurality of forcetransducers is substantially rigid and the lower plate positioned belowthe plurality of force transducers is substantially rigid.
 11. Thepatient support of claim 10, wherein the lower plate includes aplurality of standoffs, each standoff being positioned directly over acorresponding one of the plurality of force transducers.
 12. The patientsupport of claim 1, wherein the controller is operable to automaticallydetermine the value for total body weight of a person by using a look uptable.
 13. The patient support of claim 1, wherein the controller isoperable to automatically determine the value for total body weight of aperson by using a mathematical equation.
 14. The patient support ofclaim 1, wherein at least one of the head section, the seat section, andthe foot section comprises a foam material.
 15. The patient support ofclaim 1, wherein the inflatable cell is situated within the seatsection.
 16. The patient support of claim 4, wherein the inflatable cellis situated within the seat section.
 17. The patient support of claim16, wherein the second inflatable cell is situated within the headsection.
 18. The patient support of claim 1, wherein the inflatable cellis situated outside the mattress and adjacent the seat section.
 19. Thepatient support of claim 7, wherein the plurality of force transducersof the force sensor comprises a plurality of a plurality of load cells.20. The patient support of claim 7, wherein the plurality of forcetransducers of the force sensor each comprise resistive ink.